Filters
Nowadays there are a multitude of different designs of fish tank filters available. Sometimes the choice can be overwhelming. It is important that you choose a filter that is the most suitable for your tank. By tank, I don't just mean its physical characteristics - the overall environment within is what we are looking to match our filter to. Although there is a plethora of filters available out there, they can be narrowed down to just three main types. Internally, you can have either a sump tank filter or an under gravel filter. Then you have the choice of an external filter.
The sump tank filter is perhaps more suited to the marine tank, rather than the tropical, but in essence they consist of a tube which removes water from the tank to a sump area. Here is it then filtered in order to remove solid material and any harmful bacteria. This clean water is then pumped back to the tank to provide a cycle of filtered water. The under gravel filter makes use of the tank gravel as the filter. Put simply, the gravel sits on a grate and then water is sucked through it and then pumped back in at the water's surface to ensure a flow of water through the tank and the gravel. In essence the action of the water moving through the gravel serves to enable the bacteria, which live on the gravel to more efficiently remove harmful ammonia. Of course there is a physical element to this, and over time your gravel will become clogged with solid material, thus reducing the effectiveness of the bacteria and requiring you to clean it.
An external filter will (obviously) remove water from the tank, do its job and then return the filtered water back in to the tank. These are the best type of filter, but they are also the most expensive. You are then looking at making some form of trade-off - cost versus effectiveness. Having your filter outside of the tank allows you to reduce the amount of physical cleaning that you are required to do (e.g. of the gravel), but of course there is the cost associated with this.
As usual, the best advice comes from people who actually have happy and healthy colonies of fish in their tanks. Naturally, these are the people to whom you need to speak. Buying a book on the subject is all well and good, but it maybe out-dated. However, that said, the physical and biological process that go on in a tank have been known for a long time, it is perhaps only the way in which we assist them which is subject to change.
